The invention relates to an electro-optical device for the electrodynamic control of the position of a radiation spot in two directions relative to an information structure of a moving information carrier, namely, in a first direction for focusing the radiation spot on the information structure and in a second direction in a plane perpendicular to the first direction for following a track of the information structure.
A lens system is rigidly secured to a lens mounting which is pivotable to a limited extent relative to the frame about a pivotal axis parallel to and spaced from the optical axis and which is also translatable to a limited extent along the pivotal axis. Supporting means which enable movement of the lens mounting to be made include a bearing pin whose axis forms the pivotal axis and at least one bearing in which the bearing pin fits. Electromagnetic first and second actuator means effect translating the lens mounting along and pivoting it about the pivotal axis, respectively.
Such an electro-optical device for use in an optical record player is disclosed in European Patent Application No. 0068757. The lens system is arranged eccentrically in an end wall of a lens mounting comprising the end wall and a cylindrical sleeve adjoining this end wall. A sleeve bearing extends from the end wall in an axial direction and is slidable on the bearing pin. The cylindrical sleeve is axially movable and pivotable about the pivotal axis in an air gap between portions of a stator yoke which forms part of the actuator means. This stator yoke is provided with an annular permanent magnet and the stator cooperates with moving actuator means on the lens mounting. These means comprise a coil wound around the cylindrical sleeve for the axial movements and four rectangular coils which are secured to the cylindrical sleeve by an adhesive and which are bent to match the shape of the cylindrical sleeve for the pivotal movements of the lens mounting.
In general this type of electro-optical device must have a large dynamic bandwidth in order to guarantee a satisfactory control of the position of the radiation spot. A large dynamic bandwidth is also important for another reason. The susceptibility of the device to shocks exerted on it decreases as the dynamic control system is capable of more rapidly eliminating the error in the position of the radiation spot caused by the shock. Particularly, if the electro-optical device is incorporated in, for example, an optical audio record player, used in a vehicle the significance of this second reason will become more apparent. The electro-optical device described is susceptible to external shocks and is slow due to the eccentric position of the lens system and due to the concentration of a substantial part of the mass of the lens mounting in the cylindrical sleeve. Therefore, in order to reduce the effect of external shocks more power is required than is desirable. A low power is desirable in view of the heat dissipated in the coils and the dimensioning of the required control circuitry. Moreover, the known device is of intricate construction.